The present invention relates generally to high-speed contact printing technique for duplicating video information recorded on a master tape. More specifically, the invention relates to a method and device for recording control signals on a sub-master tape, e.g. a mirror sub-master tape duplicated from a master tape. In more detail, the invention relates to a method and to circuitry specifically designed to record control signals on a mirror sub master tape while eliminating noise spikes from control signals picked up off a slave tape on which the video information is to be printed by high-speed contact printing.
Contact printing is a well-known technique for video information duplication. As is well known, contact printing involves establishing close contact between a sub-master tape and a slave tape and applying a printing bias, in particular a magnetic printing bias, thermal printing bias or the like. In contact printing, video information including control signals is copied from a mother tape to a slave tape at a relatively high speed.
A mirror sub-master tape has to be prepared for contact printing. The track pattern of this mirror tape is the reverse of the normal video tape track pattern so that the normal track pattern reappears on the slave tape.
The control signals recorded on the control signal track of the slave tape are generally in the form of rectangular pulses. When these rectangular-pulse control signals are duplicated from a slave tape, the waveform on the reproduced signal is differentiated so that rising edges of the master become spikes and so on. The reproduced control signal spikes tend to be accompanied by harmonic noise at their leading and trailing edges. This noise can cause mis-triggering which may cause errors in tracking or in tape speed selection.